Key term
WJEC A-Level Biology 601-5290-0
Chemical Elements Are Joined Together to Form Biological Compounds
Topic overviewInorganic IonsBiological Importance of WaterCarbohydrates: Monosaccharides and DisaccharidesCarbohydrates: Polysaccharides and Alpha/Beta Glucose IsomerismLipids: Triglycerides and PhospholipidsLipids: Saturated and Unsaturated Fat in Human HealthAmino Acids and Proteins: Primary to Quaternary StructureAmino Acids and Proteins: Fibrous and Globular FormsCondensation and Hydrolysis: Peptide and GlycosidicFood Tests for Biological Molecules
Cell Structure and Organisation
Topic overviewEukaryotic Cell Ultrastructure: OrganellesEukaryotic Cell Ultrastructure: FunctionsProkaryotic Cells, Viruses and Cell Theory: Comparing Cell StructuresProkaryotic Cells, Viruses and Cell Theory: Electron MicrographsLevels of Organisation and Light Microscopy: Tissues and OrgansLevels of Organisation and Light Microscopy: Organ Systems and Microscope CalibrationLevels of Organisation and Light Microscopy: Magnification and Scientific Drawing
Cell Membranes and Transport
Topic overviewPlasma Membrane Structure and Permeability: Fluid-Mosaic ModelPlasma Membrane Structure and Permeability: Factors Affecting PermeabilityTransport Across Membranes: Diffusion, Osmosis and Water PotentialTransport Across Membranes: Facilitated Diffusion, Active Transport and PinocytosisTransport Across Membranes: Phagocytosis and Exocytosis
Biological Reactions Are Regulated by Enzymes
Topic overviewEnzymes as Biological Catalysts: Metabolism, Extracellular Action and Induced FitEnzymes as Biological Catalysts: Activation EnergyFactors Affecting Enzyme Activity: Temperature and SubstrateFactors Affecting Enzyme Activity: Enzyme Concentration, Denaturation and BuffersEnzyme InhibitionImmobilised Enzymes in Industry
Nucleic Acids and Their Functions
Topic overviewNucleotides, Chemical Energy and ATP: StructureNucleotides, Chemical Energy and ATP: Role as Energy CarrierDNA and RNA StructureSemi-conservative Replication, Meselson and Stahl experimentThe Genetic Code: Triplet CodeThe Genetic Code: Exons and IntronsProtein Synthesis: Transcription, Translation and tRNAProtein Synthesis: One Gene-One Polypeptide and Polypeptide Modification
Genetic Information Is Copied and Passed on to Daughter Cells
Topic overviewThe Cell Cycle and Mitosis: Interphase and StagesThe Cell Cycle and Mitosis: Cytokinesis, Significance in Renewal and RepairThe Cell Cycle and Mitosis: Root Tip Squash and Mitotic IndexMeiosis: Meiosis I and Meiosis II, crossing over and independent assortmentMeiosis: differences from mitosis
All Organisms Are Related Through Their Evolutionary History
Topic overviewClassification: Hierarchical Groups, Need and Tentative NatureClassification: Three Domains and Five KingdomsAssessing RelatednessSpecies Concept and Binomial SystemBiodiversity and Its Assessment: Habitat LevelBiodiversity and Its Assessment: Genetic Level and Molecular LevelNatural Selection as the Source of Biodiversity and Anatomical, Physiological and Behavioural Adaptations
Adaptations for Gas Exchange
Topic overviewSurface Area to Volume Ratio and Gas Exchange in Small Organisms: AmoebaSurface Area to Volume Ratio and Gas Exchange in Small Organisms: Flatworm and EarthwormSpecialised Respiratory Surfaces and Ventilation in Bony Fish: Counter-currentSpecialised Respiratory Surfaces and Ventilation in Bony Fish: Parallel FlowGas Exchange in Terrestrial Animals: Human Breathing SystemGas Exchange in Terrestrial Animals: VentilationGas Exchange in Terrestrial Animals: the Insect Tracheal SystemThe Angiosperm Leaf: StructureThe Angiosperm Leaf: Photosynthetic RoleThe Angiosperm Leaf: Stomatal Control of Gas Exchange
Adaptations for Transport
Topic overviewVascular Systems Across Animal Groups: Earthworm and InsectVascular Systems Across Animal Groups: Fish and MammalThe Mammalian Heart and Circulation: Blood Vessels and Cardiac CycleThe Mammalian Heart and Circulation: Sino-atrial Node, Purkyne Fibres and ElectrocardiogramsBlood and the Transport of Respiratory Gases: Erythrocytes, Plasma and Dissociation CurvesBlood and the Transport of Respiratory Gases: Bohr Effect and Chloride ShiftTransport of Nutrients, Hormones, Excretory Products and HeatTissue Fluid, Lymph and OedemaWater Uptake and Movement Through the Root: Dicotyledon Root Structure and ApoplastWater Uptake and Movement Through the Root: Symplast, Vacuolar Pathways and EndodermisXylem, the Transpiration Stream and Plant Water Adaptations: Cohesion-Tension TheoryXylem, the Transpiration Stream and Plant Water Adaptations: Hydrophytes and XerophytesPhloem Structure and Translocation from Source to Sink: Mass Flow ModelsPhloem Structure and Translocation from Source to Sink: Experimental Evidence
Adaptations for Nutrition
Topic overviewModes of Nutrition: Autotrophic, Heterotrophic and HolozoicModes of Nutrition: Parasitic, and Digestion in Amoeba and Hydra to Tube GutsThe Human Gut: Adaptations to an Omnivorous DietThe Human Gut: EnzymesThe Human Gut: ConditionsHerbivore, Carnivore and Parasite Adaptations: Guts and DentitionHerbivore, Carnivore and Parasite Adaptations: Ruminants, Taenia and Pediculus
Importance of ATP
Photosynthesis Uses Light Energy to Synthesise Organic Molecules
Topic overviewChloroplasts and Light Harvesting: Distribution and TransductionChloroplasts and Light Harvesting: Pigments and WavelengthsChloroplasts and Light Harvesting: Chromatography of PigmentsThe Light-dependent Stage: Cyclic and Non-cyclic PhotophosphorylationThe Light-dependent Stage: Photolysis and Reduction of NADPThe Light-independent Stage: Rubisco, Glycerate-3-phosphate and Triose PhosphateThe Light-independent Stage: RuBP Regeneration, Synthesis of Carbohydrates and Amino AcidsLimiting Factors in PhotosynthesisInvestigating the Rate of Photosynthesis and the Role of NitrogenMagnesium in Plant Metabolism
Respiration Releases Chemical Energy in Biological Processes
Topic overviewGlycolysis, Acetyl Coenzyme A and the Krebs Cycle: Triose Phosphate and PyruvateGlycolysis, Acetyl Coenzyme A and the Krebs Cycle: Reduced NAD, FAD as Electron and Proton SourcesEnergy Budgets of Aerobic and Anaerobic Glucose BreakdownUse of Lipids and Amino Acids in RespirationMeasuring the Rate of Respiration in Yeast
Microbiology
Population Size and Ecosystems
Topic overviewPopulation Growth and Its Regulation: Birth and ImmigrationPopulation Growth and Its Regulation: Emigration, Competition and Carrying CapacityPopulation Growth and Its Regulation: Density Dependent and Density Independent FactorsSampling Techniques for the AbundanceDistribution of Organisms in a HabitatHabitats, Communities and Sun as Energy SourceBiomass, Productivity and Transfer Through Trophic LevelsSuccession: Secondary Succession and PioneersSuccession: Seres and Climax CommunitiesNutrient Cycles and Human Impact: Organic Breakdown and Carbon CycleNutrient Cycles and Human Impact: Climate Change, Nitrogen Cycle and NitrificationNutrient Cycles and Human Impact: Fertilisers and Eutrophication
Human Impact on the Environment
Homeostasis and the Kidney
Topic overviewHomeostasis: Dynamic Equilibrium, Negative Feedback and Positive FeedbackKidney and Nephron Structure and Function: Nephron Structure and UltrafiltrationKidney and Nephron Structure and Function: Selective ReabsorptionKidney and Nephron Structure and Function: Nitrogenous Excretion and Kidney Practical WorkHormonal Control of Water Balance: ADH and OsmoreceptorsThe Loop of Henle, Excretory Adaptations and Kidney FailureTreating Kidney Failure: Dialysis and Transplants
The Nervous System
Topic overviewOrganisation of the Nervous Response: Receptors to Effectors and Spinal CordOrganisation of the Nervous Response: Spinal Nerves, Dorsal and Ventral RootsOrganisation of the Nervous Response: Simple Reflex Arc and the Cnidarian Nerve Net ComparedNeurones and the Nerve Impulse: Motor Neurone Structure and NatureNeurones and the Nerve Impulse: Transmission of the Impulse and Oscilloscope TracesNeurones and the Nerve Impulse: Speed of ConductionSynapses: Structure and Synaptic TransmissionSynapses: Effects of Organophosphates and Psychoactive Drugs
Sexual Reproduction in Humans
Topic overviewHuman Reproductive Systems and Gametogenesis: Ovary and Testis HistologyHuman Reproductive Systems and Gametogenesis: Spermatogenesis and OogenesisHuman Reproductive Systems and Gametogenesis: Fertilisation and ImplantationEndocrine Control of Reproduction: Menstrual CycleEndocrine Control of Reproduction: Menstruation, Pregnancy and BirthEndocrine Control of Reproduction: Birth, Lactation and Role of the Placenta
Sexual Reproduction in Plants
Inheritance
Topic overviewMendelian Inheritance: AllelesMendelian Inheritance: Monohybrid Crosses with CodominanceMendelian Inheritance: Dihybrid Crosses with LinkageTesting Genetic Outcomes and Sex Linkage: Chi-squared TestTesting Genetic Outcomes and Sex Linkage: Haemophilia and Duchenne Muscular DystrophyMutation and Control of Gene Expression: Sickle Cell AnaemiaMutation and Control of Gene Expression: Down's Syndrome and MutagensMutation and Control of Gene Expression: Carcinogens, Oncogenes and Epigenetics
Variation and Evolution
Topic overviewVariation and Selection Pressures: Genetic, Environmental Causes and ContinuousVariation and Selection Pressures: Discontinuous, Non-heritable Variation and Intra-specific CompetitionVariation and Selection Pressures: Selective AgenciesPopulation Genetics: Gene Pool, Genetic Drift and Changing Allele FrequenciesPopulation Genetics: Hardy-Weinberg PrincipleIsolationSpeciation and Darwin's Theory of Evolution
Application of Reproduction and Genetics
Topic overviewGenome Sequencing and Its Ethics: Human Genome Project and 100K Genome ProjectGenome Sequencing and Its Ethics: Genomes of Other Organisms and Screening of EmbryosGenetic Fingerprinting and Recombinant DNA TechnologyGenetic Fingerprinting and Recombinant DNA Technology: Electrophoresis and Bacterial PlasmidsGenetic Fingerprinting and Recombinant DNA Technology: Insulin and GM CropsGene TherapyGenomics in Future Healthcare and Use of Stem Cells
DiseaseOption A
AntibioticsOption A
Immune ResponseOption A
Topic overviewNon-specific Defences: Skin Flora, Connective Tissue and InflammationNon-specific Defences: Phagocytosis, Clotting and Ciliated EpitheliumSpecific Immunity: Development of Responses to Foreign Antigens and HumoralSpecific Immunity: Cell-mediated Immunity, Roles of T and B LymphocytesActive and Passive ImmunityImmunisation Programmes, Effectiveness and Ethics
Skeletal TissuesOption B
Topic overviewCartilage and Compact Bone: Hyaline and Yellow ElasticCartilage and Compact Bone: White Fibrous Cartilage, Organic and Inorganic Matrix ComponentsCartilage and Compact Bone: Haversian SystemsBone Remodelling and Bone Disorders: Osteoblasts, Osteoclasts and RicketsBone Remodelling and Bone Disorders: Osteomalacia, Osteoporosis and Brittle Bone DiseaseSkeletal Muscle: Structure and UltrastructureSkeletal Muscle: Sliding Filament Theory and FastSkeletal Muscle: Slow Twitch Fibres and Creatine PhosphateSkeletal Muscle: Lactic Acid and Energy Sources
Structure and Function of Human SkeletonOption B
JointsOption B
The BrainOption C
Topic overviewStructure and Functions of the Human Brain: Cerebrum, Hypothalamus and HippocampusStructure and Functions of the Human Brain: Cerebellum and Medulla OblongataSympathetic Nervous SystemParasympathetic Nervous System and Hypothalamus as the Nervous-Endocrine LinkThe Cerebral Cortex: Sensory and Motor AreasThe Cerebral Cortex: Motor Homunculi, Language and Speech Areas
NeuroscienceOption C
BehaviourOption C
Topic overviewInnate and Learned Behaviour: Escape Reflexes and KinesesInnate and Learned Behaviour: Taxes in WoodliceInnate and Learned Behaviour: Habituation, Imprinting and Operant ConditioningSocial Behaviour: Primate Societies, Advantages and Disadvantages of Group LivingSocial Behaviour: Insect Caste Systems and Vertebrate Dominance HierarchiesTerritorial and Courtship BehaviourRole of Sexual Selection in Their Evolution
Working Scientifically: Practical Skills
Topic overviewThe A2 Unit 5 Practical Examination Tasks: Experimental TaskThe A2 Unit 5 Practical Examination Tasks: Practical Analysis TaskIndependent Thinking and Use of Scientific Methods and Practices: Solving Problems in Practical ContextsIndependent Thinking and Use of Scientific Methods and Practices: Identifying and Following InstructionsIndependent Thinking and Use of Scientific Methods and Practices: Making and Keeping RecordsIndependent Thinking and Use of Scientific Methods and Practices: Presenting DataNumeracy in Practical Contexts, Research and Referencing: Plotting, Interpreting Graphs and ProcessingNumeracy in Practical Contexts, Research and Referencing: Analysing Data, Margins of Error and AccuracyNumeracy in Practical Contexts, Research and Referencing: Precision and OnlineNumeracy in Practical Contexts, Research and Referencing: Offline Research Skills
Use of Apparatus and Techniques
Topic overviewMeasurement and Laboratory Technique: Quantitative ApparatusMeasurement and Laboratory Technique: InstrumentationMeasurement and Laboratory Technique: Glassware Including Serial DilutionsMicroscopy, Scientific Drawing and Separation and Identification Techniques: Light MicroscopeMicroscopy, Scientific Drawing and Separation and Identification Techniques: Annotated Drawings and Food TestsMicroscopy, Scientific Drawing and Separation and Identification Techniques: ChromatographyWorking with Organisms and Aseptic TechniqueViable Counts, Dissection and Fieldwork SamplingMark-Release-Recapture, Quadrats and ICT for Data Collection
Mathematical Requirements (Appendix C)
Topic overviewArithmetic and Numerical Computation: Appropriate Units, Decimal and Standard FormArithmetic and Numerical Computation: Ratios, Percentages and Estimating ResultsArithmetic and Numerical Computation: Power, Exponential and Logarithmic FunctionsHandling Data: Significant Figures, Arithmetic Means and MeanHandling Data: Median, Frequency Tables and HistogramsHandling Data: Scatter DiagramsProbability, Sampling, Statistical Tests and Uncertainty: Simple Probability and SelectingProbability, Sampling, Statistical Tests and Uncertainty: Using the Chi-squared TestProbability, Sampling, Statistical Tests and Uncertainty: Correlation CoefficientProbability, Sampling, Statistical Tests and Uncertainty: Standard DeviationAlgebra and Magnification: Mathematical Symbols and Changing the Subject of an EquationAlgebra and Magnification: Substituting Values, Solving Equations and Using LogarithmsGraphs: Translating Between Graphical, Plotting Two Variables and Linear RelationshipsGraphs: Intercepts, Rate of Change and Slope of a Tangent to a CurveGeometry: Circumferences, Surface Areas and Volumes of Regular Shapes
How Science Works (Appendix D)
Topic overviewDeveloping and Communicating Scientific Explanations: Using Theories, Models and IdeasDeveloping and Communicating Scientific Explanations: Posing Scientific QuestionsScientific Methodology, Evidence and Evaluation: Appropriate Methodology Including ICTScientific Methodology, Evidence and Evaluation: Analysing and Conflicting DataScience, Society and Ethics: How Scientific Knowledge Develops Over TimeScience, Society and Ethics: Risks, Ethical Treatment of Humans and Other OrganismsScience, Society and Ethics: Environment and How Society Uses Science
Inheritance
Testing Genetic Outcomes and Sex Linkage: Haemophilia and Duchenne Muscular Dystrophy
- 3 things to know
- A2 Unit 4
Overview
Recall questions on Haemophilia and Duchenne Muscular Dystrophy.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
Why does a male carry only one allele of an X-linked gene?
Key term
Explain why X-linked recessive conditions are far more common in males than females.
Questions from this subtopic
Each one with the model answer underneath.
- 1
Define sex linkage.
Model answer
Sex linkage is the carrying of a gene on a sex chromosome, so that the pattern of inheritance differs between males and females.
- 2
Why does a male carry only one allele of an X-linked gene?
Model answer
The Y chromosome is much shorter and carries no equivalent allele, so the single allele on the X chromosome is always expressed.
- 3
Explain why X-linked recessive conditions are far more common in males than females.
Model answer
A male needs only one copy of the recessive allele to be affected, whereas a female must inherit two copies.
- 4
Can a father pass an X-linked allele to his son? Explain your answer.
Model answer
No, because a son inherits the Y chromosome from his father and his single X chromosome from his mother.
- 5
What is meant by a carrier of an X-linked condition?
Model answer
A carrier is a heterozygous female who has the recessive allele but does not show the condition.
- 6
How is the genotype of a female carrier of haemophilia written?
Model answer
It is written Xᴴ Xʰ, with superscripts showing the alleles carried on each X chromosome.
Other ways to work this
The same content, four other ways.
What is inside Levo
Six ways to work the same material.
Every question in Inheritance, on a schedule.
Attempt a question from memory, write the correct version, then attempt it again. Levo records the jump between your first attempt and your last, and brings each question back on the day you are due to forget it.
Or £46 a year, about £3.83 a month. Cancel anytime.